Certain downhole operations involve placement of elements in a downhole environment, where the element performs its function, and is then removed. For example, elements such as ball/ball seat assemblies and fracture (frac) plugs are downhole elements used to seal off lower zones in a borehole in order to carry out a hydraulic fracturing process (also referred to in the art as “fracking”) to break up reservoir rock. After the fracking operation, the ball/ball seat or plugs are then removed to allow fluid flow to or from the fractured rock.
To facilitate removal, such elements may be formed of a material that reacts with the ambient downhole environment so that they need not be physically removed by, for example, a mechanical operation, but may instead corrode or dissolve under downhole conditions. However, because operations such as fracking may not be undertaken for months after the borehole is drilled, such elements may have to be immersed in downhole fluids for extended periods of time (for example, up to a year, or longer) before the fracking operation begins. Therefore, it is desirable to have corrodible downhole elements such as ball seats and frac plugs that are protected from uncontrolled corrosion during that period of time, and which then can be subsequently made corrodible as needed.